The approval rating of software entrepreneur-turned-professor Ahn Cheol-soo climbed five percentage points last week to match those of presidential frontrunner Park Geun-hye, a poll showed Monday.

Ahn has not officially declared a bid for the presidency, but is widely regarded as a serious opposition contender against Park from the ruling Saenuri Party in December's presidential election.

That possibility strengthened when Ahn's new book, "Ahn Cheol-soo's Thoughts," and his appearance on a TV talk show generated explosive responses from the South Korean public.

The book, released on July 19, became an immediate bestseller, while the hour-long TV interview, aired four days later, recorded the highest viewer rating for the show at 18.7 percent nationwide and 21.8 percent in the capital area, according to AGB Nielsen Media Research.

In a survey of 1,520 people conducted from Monday through Friday of last week, Ahn and Park each got approval ratings of 42 percent, according to polling agency Gallup Korea. That figrue was a three-percentage-point decrease for Park, but a five-percentage-point increase for Ahn from the previous week.

Park maintained a lead of up to 10 percentage points at around 47 percent in May and June, before Ahn stepped back into the media spotlight.

The professor first demonstrated his political influence last October when his backing was viewed as helping an independent candidate become mayor of Seoul.

Ahn has since remained ambiguous about any presidential ambitions, but disclosed in his book and on the talk show that the opposition's surprise defeat in April's parliamentary elections made him seriously consider running for the top political job.

In a multi-way race with other presidential hopefuls, Park took the top spot with 38 percent, followed by Ahn with 29 percent and Moon Jae-in, a leading contender of the main opposition Democratic United Party, with 11 percent, according to the poll.

However, those results were most favorable to Ahn, as his rating increased eight percentage points from the previous week, while Park's rose only one percentage point and Moon's dropped four percentage points.

The survey had a margin of error of plus or minus 2.5 percentage points at a 95 percent confidence level.

A former medical doctor and the founder of anti-virus software firm AhnLab, Ahn currently serves as dean of the Graduate School of Convergence Science and Technology at Seoul National University. He is widely popular, especially among young Koreans, due largely to his clean and upright image. (Yonhap News)